Document-generating is implemented by a number of hard copy output devices such as printers, copy machines, facsimile machines and multiple function peripheral (MFP) devices. In order to generate hard copy output, a supply of printable media needs to be made available to such devices. Typically, a stack of paper, or media, is supplied to a device from one or more removable paper trays. A host computer, or external device, submits a print, copy or facsimile job to the device which includes commands that tell the device on which size paper to print the job.
In order to determine the size of paper, or media, present within the paper tray of these devices, some technique is needed to detect the size of paper, or media, present in the supply tray.
Several techniques are known for conveying to a printing device information about the contents of a paper tray. According to one prior art technique, a uniquely sized tray is provided for each paper size that is accommodated by a printing device. For example, one tray is sized to receive letter-sized paper, while another tray is sized to receive legal-sized paper. Insertion of a specific size tray ensures only that size paper will be used. Accordingly, insertion of the specific size tray by a user notifies the user as to which sized paper is presently available. Optionally, a selection switch can be provided on the printing device that is set by a user to the paper size currently loaded in the device. Alternatively, mechanical identification features have been provided on a tray which are detected by the device once the tray is inserted, thereby identifying the specific paper size to the device. However, it is costly and inconvenient to utilize several different size trays. Additionally, storage space is needed to store the surplus trays.
According to another technique, a single paper tray can be reconfigured to receive various sizes of paper. Many home and small-business printers utilize such a single paper tray. However, re-configuration only accommodates a series of discrete paper sizes, such as letter-sized, legal-sized and A4-sized paper. Typically, a series of notches or holes is provided in the tray, and one or more media stops are positioned into a selected set of notches or holes to accommodate one of the available paper sizes. However, only a handful of predefined discrete paper sizes is available.
According to yet another technique, a single paper tray is reconfigured by a user after purchase to accommodate a single size of paper. According to such technique, the single paper tray is molded to accommodate a large selection of readily available paper sizes. The user indicates to a printer the size of paper that is present in the tray. One technique for indicating to the printer the size of paper involves "punching out" a marker or location in the paper tray corresponding to the specific paper size. A sensor detects the "punched out" marker which notifies the printer of the specific paper size. However, once punched out the tray is permanently configured for that particular paper size. The user must purchase a new tray in order to use a different paper size.
According to even another technique, U.S. Pat. No. 5,483,889 discloses an automatic media size detector for use with paper trays to detect the size of media present in a paper tray. A back stop and a side stop are each moved to unique associated receiving positions that are provided in the paper tray, with each position corresponding to a specific paper size. A plurality of conductive strips are provided in the tray, in proximity with each back stop. Each back stop, when received in an associated receiving position, makes electrical contact between a unique pair of the conductive strips so as to electrically connect the strips. The printer, using a look-up table, monitors all the strips to determine which two strips of the plurality are electrically connected together, which also indicates the received paper size. However, only a limited number of preselected paper sizes can be accommodated by such a paper tray.
Therefore, there exists a need for an improved automatic media size detector capable of detecting an infinite number of media sizes within a range of sizes. Furthermore, there is a need for an improved paper tray utilizing such a media size detector.